Implantable medical devices generally include a hermetically sealed metal case or can. For implantable cardiac rhythm management devices, electrical signals sensed in the body and electrical signals delivered to the body need to pass through the hermetic seal. These electrical signals must pass through the hermetic seal of the device and yet be insulated from the metal case. This is accomplished with feedthroughs. Feedthroughs are comprised of an electrical conductor, usually a pin, passing through insulating material and providing connection from circuitry internal to the can to a point external to the can while maintaining the hermetic seal.
Electromagnetic signals from external electrical sources encountered in a patient's normal environment can also pass through the feedthrough and interfere with proper operation of the implantable device. Consequently, electromagnetic interference (EMI) filters are provided to prevent unwanted electromagnetic signals from being sensed by the device and interfering with its normal operation. For cardiac rhythm management devices these filters must be designed to withstand electrical signals of several hundred volts that can be encountered during electrocautery, external defibrillation or internal defibrillation if the device is an implantable defibrillator. Also, the filters must also be located as close as possible to the hermetic seal to prevent or minimize entry of the signals into the metal case.
Often, the EMI filters are comprised of capacitors provided with the feedthroughs as a custom designed assembly. The assemblies are extremely costly due to the complex processes required in their manufacture. Also, interconnecting the custom filtered feedthroughs and the rest of the assemblies in the device are often difficult to control effectively. One result is that it is difficult to obtain and maintain sources for the filtered feedthrough. What is needed is an assembly that meets the design challenges required of filtered feedthroughs for medical devices yet reduces cost and increases their availability.